Sodium and potassium metals supported on potassium carbonate carriers are known to be effective catalysts for the dimerization of propylene to 4-methyl-1-pentene, which is a useful comonomer in polymer synthesis. The same catalysts are effective in codimerizations. Unsupported sodium and potassium catalysts, however, give unsatisfactory polymerization rates, have poor selectivities, or do not demonstrate adequate catalyst life. The sodium and potassium catalysts, which utilize potassium carbonate supports, give a better performance than the unsupported metals, but have poor strength and are subject to undesirable attrition and the generation of fines during use and handling. These deficiencies result in poor economics due to catalyst losses and excessive pressure drops in the reactor.